1. Field of the Invention
The present invention relates to functionalized styrene derivatives containing carbazole and their anionic polymerization. More specifically, the present invention relates to styrene derivatives containing carbazole, and an improvement in the thermal stability, optical properties, and molecular weight and molecular weight distribution of homopolymers or copolymers of the styrene derivatives, along with the anionic polymerization method. The term, optical properties, as used herein include photoluminescence and photoconductivity.
2. Description of the Prior Art
Carbazole-containing materials have been widely used as photoconductive, refractive and non-linear optical materials, and have been recently reported to be useful as media of photoluminescence materials [(1) Y. Zhang, T. Wada, and H. Sasabe, Chem. Commun., 1996, 621. (2) Y. Zhang, T. Wada, and H. Sasabe, Macromol. Chem. Phys., 1996, 197, 667. (3) K. Tamura, A. B. Padias, H. K. Hall Jr., and N. Peyghambarian, Appl. Phys. Lett., 1992, 60, 1803.].
In addition, it is reported that carbazole-containing materials, together with associated metals, have been used as polymers for electrophotoluminescence [A. Ribou, T. Wada, and H. Sasabe, Inorganica Chemica Acta, 1999, 288, 134].
The photorefractive polymers must preferably have low glass transition temperature, while the electrophotoluminescent polymers must preferably have high glass transition temperature in consideration of thermal stability. Therefore, if glass transition temperature can be controlled by the molecular weight of the polymers, the polymers can be used for various applications.
Since anionic polymerization of styrene has been found, researches have been actively carried out. Recently, anionic polymerization techniques have been developed, so styrene can be prepared in large scale through such polymerization at plants.
However, in the case of styrene with functional groups, undesirable side-reactions occur during the polymerization. In this regard, it is reported that, in styrene derivatives with functional electron donating groups to the para-position, side-reactions are caused so that molecular weight and molecular weight distribution of the polymer cannot be controlled [T. Ishizone, T. Utake, Y. Ishino, A. Hirao, and S. Nakahama, Macromolecules, 1987, 30, 6548]. Furthermore, when methylene group is introduced into styrene as a functional group, highly reactive chain ends of the polymer attack methylene group during polymerization, thus it is not easy to obtain well-controlled polymers.
Much efforts have been directed toward successfully synthesizing polymers by introducing a functional group-protecting group to the polymerization reaction, and then removing the protecting group after the polymerization [T. Ishizone, G. Uehara, A. Hirao, S. Nakahama, and K. Tsuda, Macromolecules, 1998, 31, 3764].
When monomer is in a liquid state, pure monomer can be obtained by distillation or other processes, while monomer of solid state has some impurities because distillation cannot be performed in a vacuum. Hence, such impurities reduce activity of starting materials, and consequently molecular weight and molecular weight distribution of the polymer cannot be easily controlled.
Accordingly, an object of the present invention for alleviating the problems as described above is to provide a polymer and a method for synthesizing the same, in which a carbazole-containing solid styrene monomer is used at lowered reaction temperature which restrains side-reactions, so that a homopolymer with defined molecular weight and limited molecular weight distribution is resulted, and such homopolymer and a carbazole-containing styrene derivative are block-copolymerized with other monomers, thereby obtaining a polymer with defined molecular weight.